It has been known that certain types of alkaline cleaners are effective compositions for "pretreating" soiled pots, pans, plates and other eating utensils. These cleaners are applied to the utensils after use and allowed to remain on the utensils for from 5, preferably from 10 minutes, to about 1 hour. After this pretreatment, food soils are easily removed by light washing from the utensils: little scrubbing is required as mere rinsing or light rubbing with a sponge or cloth removes all food soil. These pretreating compositions even loosen and remove burned-on, dried or cooled food substances, including those such as chocolate and tomato sauce that are known as difficult to remove.
U.S. Pat. No. 4,105,574 (Culmone) and U.S. Pat. No. 4,372,788 (Lancz) describe "grill" and "oven" cleaners based on monoethanolamine. U.S. Pat. No. 4,056,113 (Johnson et al.) and U.S. Pat. No. 4,268,406 (O'Brien et al.) describe liquid dishwashing detergent compositions containing free monoethanolamine and which are noted to be particularly suited for removing cooked-on foods from cooking utensils.
These compositions are usually applied directly to the soiled area of the utensil without dilution. Filling a pot or pan with water before or after adding the pretreater will usually reduce the effectiveness of the cleaner.
A common problem with these pretreating products, however, is that they stain cooking and eating utensils which contain aluminum. It has been estimated that 10% of flatware and around 50% of pots and pans contain aluminum. The usefulness of these pretreating compositions is reduced by the large black expanses, the numerous irregular black patches or the many tiny black dots with which pretreaters may stain a utensil.
The alkalinity of the pretreating compositions causes the stains or discoloring. Alkalinity though is very desirable in these products for soaking into burned-on or dried food and loosening the same from pans or utensils.
To preserve the alkalinity of pretreating products but avoid staining utensils, several anti-stain agents such as colloidal and fumed silicas have been tried. Colloidal silicas did not prevent staining by the high electrolyte pretreating composition because they caused agglomeration and instability. Various fumed silicas were more successful: low levels of fumed silicas did prevent staining at full strength but these silicas were of limited usefulness. Diluted to less than 10% strength, the composition with fumed silica no longer prevented staining. This is deemed a serious defect due to the practice of many consumers of mixing pretreating compositions with liberal amounts of water. Further work with fumed silicas failed to overcome the problem of aluminum staining from dilute solutions. Silicates are not generally effective in formulations and conditions of medium alkalinity (pH &lt;11) due to tendency to deposit hard-to-remove silica-containing precipitates.